   [state st]
   (assoc-in state [:cpu :st] st))
 
+(defn- update-draw-flag
+  [state draw-flag]
+  (assoc-in state [:cpu :draw-flag] draw-flag))
+
 (defn- update-stack
   ([{{:keys [stack]} :cpu :as state} idx val]
    (update-stack state (assoc stack idx val)))

  (-> state
      (assoc :screen (screen/make-screen))
      (assoc-in [:cpu :draw-flag] 1)
      (assoc-in [:cpu :pc] 2)))

(defn opcode-00EE
  "Return from a subroutine."

  (-> state
      (update-memory (vec rom) 0x200)))

;; FIXME:
(defn opcode-00E0
  "Clear the screen. This function will also set draw-flag to 1
  to make canvas function refresh."
